1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile.
2. Description of the Prior Art
FIG. 40 illustrates a mounting structure of a transparent platen on a frame in a conventional copying machine. In the conventional copying machine, a plurality of rubber plates 701 are fixed on a frame 700, and a transparent platen 702 is mounted on the frame 700 in a state where the transparent platen 702 is disposed thereon.
In the above described copying machine, external air including dust enters the copying machine from a portion between the frame 700 and the transparent platen 702, whereby the inner surface of the transparent platen 702 and an optical system for exposure are liable to be dirty. Consequently, image degradation such as fogging occurs, and toner consumption becomes larger than necessary.
If the copying machine is installed in a so-called convenience store, dust-proof measures become significantly important. The reason for this is that the convenience store is located in the place where superior conditions of location for the traffic situation are satisfied, that is, faces on a street, and the copying machine is located in the vicinity of the entrance of the convenience store, whereby the copying machine is exposed to dust and solar light in many cases.
Dust-proof measures have been conventionally taken against the optical system for exposure in the copying machine. Specifically, in order to perform development using powder toner in the copying machine, the optical system for exposure must be protected from scattering of the toner. The optical system for exposure is generally protected from scattering of toner by separating a developing section and the optical system for exposure.
On the other hand, it is considered that the optical system for exposure is trapped in a sealed space so as to reduce the effect of the change in the external environment on the optical system for exposure as well as prevent dust and the like from entering the optical system for exposure from the exterior. As a light source for exposure in the copying machine, however, a halogen lamp generating a great amount of heat is generally used, whereby the optical system for exposure must be cooled. Therefore, it is difficult cause the optical system for exposure to have a sealed structure.